The present invention relates to the structure of a brush lead used in a motor-immersed fuel pump, and particularly the present invention provides a brush lead with a structure in which at least the portion of a brush lead exposed to fuel is composed of a material which is non-reactive with the fuel, thereby fuel is free of deterioration and the brush lead is protected from erosion, which, in turn, insures the long service life of the fuel pump and high performance of an internal combustion engine to which fuel is transported by the pump.
As schematically shown in FIG. 1, a motor-immersed fuel pump is a type of fuel pump used in an engine-driven vehicle such as an automobile. Referring to FIG. 1, a motor-immersed fuel pump 1 includes a pump mechanism 2, which is of the vane type. The vane pump 2 includes a rotor 2a which is fixedly mounted on and at one end of a driving shaft 3a of a motor 3. The motor 3 is completely housed in a casing 5 and a motor chamber 4 is defined in-between. Thus, when the rotor 2a is driven to rotate by the motor 3, fuel is introduced into the motor chamber 4 through an inlet port 1a and discharged exteriorly through an outlet port 1b, as shown by the arrows. As described above, since the motor 3 is completely immersed in the flow of fuel, heat generated inside the motor 3 is carried away and the motor 3 can be maintained at low temperatures as desired. Moreover, sparks between a commutator 6 and a brush 7 are suppressed and the induced explosion of vaporized fuel by these sparks is prevented from occuring. These are the main advantages of a motor-immersed fuel pump.
It should be recalled that for the operation of the motor 3, a lead wire 8 must be provided for the electrical connection between the brush 7 and an exterior source (not shown). It is a well established practice to use copper or copper alloy as the most suitable material for the lead wire 8 for various reasons such as high electrical conductivity, excellent mechanical workability, and economical advantage. If a fuel pump is of the type in which the motor is not immersed in the flow of fuel, but rather positioned in the atmosphere, no particular problems with respect to the lead wire 8 exist. However, in the case of a motor-immersed fuel pump as shown in FIG. 1, there are disadvantages since the copper or copper alloy lead wire 8 is also immersed in the fuel, usually gasoline. In this instance, the copper ingredients in the lead wire react with gasoline so that gasoline undergoes adverse effects such as being oxidized and thus oxidized gasoline promotes the corrosion of the lead wire. Such phenomenon of the deterioration of fuel, usually gasoline, by reaction with copper ingredients, particularly copper ions, is well known.
When use is made of alcohol added gasoline, so-called gasohol, which has recently become very popular as a means to curb energy crunch problems, the reaction rate between the fuel and the copper ingredients increases markedly and there is even a possibility that the lead wire including copper as an ingredient could be partly eaten away due to extensive corrosion after short hours of service. Moreover, in order to obtain required flexibility, the lead wire is usually made by twisting or weaving a plurality of fine strand wires, rather than a single fat wire, which makes the contact area with fuel larger; therefore, the reaction rate is increased and the lead wire is easier to corrode.